The First Lord Advocate
The term "advocate" has been used in Scotland for a long time, and in the reign of Alexander the Third (crowned 1294), the right of advocates to plead was secured by law. In 1424, under James the First, it was ordained "leal and wise" that counsel should be appointed to assist poor suitors. There is no trace of a King's Advocate, but as private individuals could employ advocates to represent them, it was natural that the King should do the same. It is possible that having such an officer may have arisen from the alliance between France and Scotland, which imported many French ideas into the Scottish Courts - the equivalent to the Kings Advocate was the Procureur du Roi.
Towards the end of the fifteenth century, authentic traces of the office begin to appear. Sir John Ross of Montgrenan is the first King's Advocate whose name is known, but there is no record of his date of appointment. In June 1479 Ross was a witness to a summons against John Ellem of Butterdem, and others, for treasonably holding the Castle of Dunbar against the King. In October of that year, Ellem and his companions did not appear for trial, and the records of the Parliament show that "The Advocate" called on the House to give judgment against them. They were found guilty and their estates forfeited to the Crown. Sir John Ross is not named as advocate in the records, but in 1483, when the Duke of Albany failed to appear to answer a summons of treason, "Johne the Ross of Montgrenan, as advocat to his heines", craved the judgment of Parliament, which was given against Albany.
Ross was sent as an ambassador to the court of Henry the Seventh. He was put on the Committee, which was to care-take the functions of the Parliament until it reassembled. It did not reassemble until after the rebellion and the death of James the Third. Ross had fought during in the rebellion, but his office for the King was no defence, and the new Scottish King James the Fourth punished all those who had opposed the rebellion. Ross was charged with treason, and ordered to appear before the Parliament. He did not appear, and the Lord Chancellor moved for sentence against him. He was condemned to death, and his lands at Montgrenan were given to Patrick Hume of Fastcastell.
Ross, however, had an ally in Henry the Seventh, from his time in the English Court. Henry wrote to Pope Innocent the Eighth on Ross' behalf, stating that his only misdemeanour had been that "he adhered to his Sovereign". This intervention seems to have worked, as Ross is recorded as reappearing in the Parliament in 1489. In October 1490 he was elected one of the Lords of Council and Session, and in the following month his land and property were restored to him. He continued to transact public business until his death in 1495, although there are no records of him ever having been paid.
Ross was not a public prosecutor, as we understand it today. At that time all prosecutions proceeded at the instance of the person injured or his kinsmen. In cases of treason or blasphemy the King alone was prosecutor, and laws in 1424 and 1436 concerning danger to crops, land and people from fire, and trespassers, were also prosecuted at the King's instance. Private prosecutors appeared in person at the bar, but the King could not do so, and the duty was imposed on the Advocate, but at what exact date is not known.
After the fifteenth century the Advocate becomes a leading figure in public life in Scotland. He was not merely a law officer and took a leading part in the general business of government, probably had a seat in Parliament and undertook diplomatic business.
Reference: George W T Osmond, The Lord Advocates of Scotland from the close of the Fifteenth Century to the passing of the Reform Bill. Vol 1. David Douglas, Edinburgh, 1883